MICROSCOPIC CHARACTERISTICS OF FILLED AND EXTENDED PHENOL FORMALDEHYDE RESIN-ADHESIVE BONDS

Clay, wheat flour, and pecan shell flour are often used as fillers or extenders in adhesive systems. To explore the minute characteristics of these materials, an examination was made of raw clay, wheat flour, and pecan flour with scanning electron microscopy. The size and shape of particles were found to differ among these three materials: clay particles were small and flat; wheat particles were rather large, ovate, and dimpled; while pecan shell particles were very irregular and often displayed a layered appearance. The presence of agglomerates was also seen. Phenol-formaldehyde adhesive samples containing each of these materials were cured and fractured, revealing markedly different fracture surfaces. Unlike the other materials, the wheat particles did not appear to be intact on the fracture surface of the resin samples. Flakeboard fracture surfaces containing these resins were also examined. Clay and pecan shell particles, but not wheat particles, were observed on flakeboard fracture surfaces.